1. Field of the Invention
The present invention relates to a refrigerated centrifuge instrument and, in particular, to a refrigerated centrifuged instrument having a system for reducing the noise level associated with the operation of the centrifuge refrigeration system.
2. Description of the Prior Art
A centrifuge instrument is a apparatus adapted to expose a sample of a liquid carried within a rotating element, known as a rotor, to a centrifugal force field. FIG. 1 illustrates a highly stylized representation of a centrifuge instrument generally indicated by the reference character 10.
The centrifuge 10 includes a framework, schematically indicated by the reference character 12, that supports a bowl 14. Access to the interior of the bowl 14 is afforded through a lid 16. Sealed integrity between the bowl 14 and the door 16 is maintained by a seal 18 disposed on the periphery of the upper edge of the bowl 14.
A drive motor 22 is supported by the framework 12 beneath the bowl 14. A shaft 24 extends from the motor 22 into the interior of the bowl 14 through the opening 26. A rotor mounting element, or spud, 28 is disposed at the upper end of the shaft 24. The mounting element 28 supports a centrifuge rotor 30 thereon.
In some instances it may be necessary to refrigerate the interior of the bowl 14. To this end a refrigeration system generally indicated by the reference character 32 is provided. The refrigeration system 32 includes the series connection of an expansion valve 34, an evaporator coil 36, a compressor 38, and a condenser 40. The evaporator coil 36 is disposed in a heat transfer relationship with the exterior of the bowl 14. The condenser 40 has an associated fan 42 that is driven by a motor 44. The system 32 may include other elements, such as a filter/dryer and an expansion valve bulb with capillary tubing coil, as will be appreciated by those skilled in the art. These elements are omitted from FIG. 1 for clarity of illustration.
The temperature of the bowl 14 is monitored by a sensor 46 which provides a signal representative thereof over a line 48 to a controller 50, typically a microprocessor-based implementation. The controller 50 is connected to the drive motor 22 over a line 52, to the compressor 38 over a line 54, and to the condenser fan motor 44 over a line 56.
In response to a user-initiated start request the controller 50 verifies that no system faults are present and outputs a drive enable signal on the line 52 to assert the drive motor 22. The user also, in the typical case, requests a chamber temperature at which the centrifugation run will be performed.
Based upon the ambient temperature of the air in the bowl 14, as measured by the sensor 46, the controller 50 provides a control signal over the line 54 to assert the operation of the compressor 38, thereby to cause refrigerant to be circulated through the closed loop refrigeration system 32. In addition, a command is output from the controller 50 over the line 56 to assert the motor 44 for the fan 42, thereby to cause airflow over the condenser 40.
During periods when the instrument is not actually operating to spin a sample the air temperature within the bowl 14 is nevertheless monitored and maintained to some predetermined level in anticipation of a refrigerated run. This this period is usually termed "standby" mode. When a requirement for a lower bowl temperature is made by a user the ambient temperature of the bowl is drawn down from the standby level.
In the refrigerated instruments manufactured by the Medical Products Department of E. I. du Pont de Nemours and Company and sold as the "RC-2B" instrument and as the "RC-5B" instrument, whenever the motor 22 is asserted by the controller 50, the controller 50 simultaneously outputs a signal on the line 56 to assert the motor 44 for the fan 42. The compressor 38 is asserted as needed to hold the chamber temperature (as measured by the sensor 46) to the user-requested temperature.
It has been noticed, however, that the operation of the condenser fan 42 and its drive motor 44 are often a source of considerable noise, particularly during the standby mode. To control the noise emission caused by these elements it is also a known practice in the art to provide a thermostat 60 that monitors the temperature of the refrigerant through the condenser. Based upon this measurement a fan controller 62, typically a variable resistor arrangement, modifies the drive current applied to the fan motor over a line 64. The refrigerated instrument manufactured Andreas Hettich Company, Tuttlingen, Germany, and sold as the "Omnispin" exemplifies such a refrigeration noise control arrangement.
In view of the foregoing it is believed advantageous to provide a noise control system that minimizes the noise level associated with the assertion of the condenser fan.